Fuel compositions containing glycerol

ABSTRACT

Fuel compositions containing fuels and glycerol are disclosed. The addition of glycerol increases the combustion value of the fuels, and enables combustion to take place more uniformly and with less slag formation. The use of glycerol for improving the combustion value and combustion efficiency of liquid or solid fuels is thus also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. Section 119 of European application EP06021488.9 filed Oct. 13, 2006, the contents of which are incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This invention relates generally to oleochemical raw materials and, more particularly, to fuel compositions containing added glycerol.

BACKGROUND OF THE INVENTION

Since the beginning of industrialization, technical progress has been associated with the supply of heat and energy. Whereas, originally, being able to produce these resources in sufficient quantities and at low prices was all-important, ecological aspects above all also acquired increasing significance in the last two decades of the last century. This can be illustrated by just two examples which reflect the span between national problems and globalization in this context:

-   -   As a result of the proven connection between particulate         emissions and diseases of the respiratory tract, automobile         manufacturers have been under pressure to equip diesel vehicles         with correspondingly effective particle filters.     -   In the struggle against global warming, reducing CO₂ emissions         is a critical factor. The awarding of a limited number of         emission certificates is intended to motivate industries to         reduce emission levels voluntarily because otherwise high         additional costs will be incurred.

Other aspects concern the use of fuels which, although inexpensively available in large quantities, cannot be used for one reason or another for the generation of heat and electricity. A prominent example of this is coal dust which can only be burnt in specially designed power stations because its use always involves the risk of a fine dust explosion. Another example is the waste which accumulates in the production of polymer fibers, for example short and therefore worthless fragments of polyacrylate fibers which, hitherto, not only could not be burnt, but—on the contrary—had to be disposed of at great expense to comply with environmental laws and regulations.

Accordingly, the complex problem addressed by the present invention was to offer a uniform inventive concept for the many problems mentioned above in regard to the supply and optimization of fuels. The emphasis in this regard on the one hand would be on improving the combustion value and combustion performance of conventional raw materials, such as for example fuels or heating oils both for fixed and for mobile combustion units, and on the other hand on the provision of certain materials for burning which, hitherto, could not be burnt very economically, if at all, such as coal dust or polymer waste.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to compositions containing fuels and glycerol. The addition of glycerol to fuels affords a number of advantages and, in particular, meets the complex requirement profile discussed above. More particularly:

-   -   the addition of glycerol reduces the amount of NOX and carbon         monoxide, above all in the combustion of fossil fuels;     -   the addition of glycerol reduces the formation of soot and         particulate matter, for example in the combustion of diesel         fuels;     -   the addition of glycerol improves solubility behavior in the         case of liquid fuels;     -   the addition of glycerol reduces viscosity and improves flow         properties; for example in the case of marine diesel;     -   the use of glycerol improves the oil economy of industrial         combustion processes for generating heat and electricity,         because emission certificates do not have to be acquired for         carbon dioxide which is formed in combustion of renewable raw         materials, such as glycerol;     -   the addition of glycerol allows the use of fine-particle fuels,         such as coal dust for example, by dampening or by forming a         slurry so that the danger of dust explosions is avoided; and     -   the addition of glycerol enables waste from the polymer industry         to be used, for example by converting polyacrylate fibers into         gels or particulate products which can readily be incinerated.

The addition of glycerol means that not only is air delivered to the combustion process from outside, the “3-O-compound” glycerol also acts as an oxygen carrier, more particularly in the liquid phase, which makes combustion easier and hence also results in less soot formation.

The present invention also relates to a process for improving the combustion value and combustion performance of liquid or solid fuels which is characterized in that glycerol is added to the fuels and the resulting compositions are then subjected to combustion. The compositions can be produced in various ways which leads to different embodiments of the same process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about.”

Fuels

The generic term “fuel” in the present context encompasses any combustible, preferably solid or liquid material, which converts stored energy into useful energy by oxidation with atmospheric oxygen, generally in the form of combustion. Combustion fuels are used to generate heat whereas power fuels are used in combustion engines. This definition of fuels is independent of their chemical composition; thus, “heating oil” is a combustion fuel which is marketed as power fuel under the name of diesel. In the context of the present invention, both terms are used synonymously in case of doubt. In addition, there are natural and synthetic fuels. Natural fuels are used in the form in which they are taken from the environment. Synthetic fuels are obtained from natural fuels by individual process steps. The quality of a fuel in regard to its capacity for generating heat can be evaluated through its calorific value or its combustion value. Evaluation depends on the extent to which the water present as vapor in the waste gas is used as energy (combustion value utilization). In the case of fuels with no hydrogen (bound or as water), the numbers for combustion value and calorific value are identical.

Typical examples of liquid fuels are power fuels for spark-ignition or diesel engines, kerosene, heavy oils for powering marine diesels, heating oils and fractions which accumulate in the refining of petroleum. Typical examples of solid fuels are coal, coal dust and wood. The addition of glycerol to these fuels mainly has the advantage of improving combustion behavior and increasing the calorific or combustion value. In addition, in the case of coal dust, the risk of dust explosions is eliminated.

A special case for the use as a solid fuel is waste from the polymer industry, more particularly in the form of short fiber fragments which accumulate in the production of polyacrylates and which not only have no economic value, but also have to be disposed of at great cost. Since the fibers, which are normally used as super absorbers for diapers and the like, have a high absorption capacity for liquids, they are easily saturated with glycerol and, depending on the percentage fiber content, form gels or easy-to-shape bodies which can readily be subjected to combustion. Instead of high costs for proper disposal, credits for the combustion performance are now obtained. In addition, other suitable fuels are mixed loads for garbage incineration which naturally accumulate in indefinite quantities, especially since domestic garbage can no longer be taken to waste disposal sites. The dampening of such materials is intended above all to facilitate their burning on the grates. Untreated glycerol, for example direct from the production of biodiesel, is also suitable for this very purpose because the water content provides for calmer combustion and even the salt content is not problematic because it subsequently reappears in the slag. Further examples and data on their calorific and combustion values can be found in Table 1 below.

TABLE 1 Calorific and combustion values of liquid and solid fuels Fuel Calorific value [MJ/kg] Combustion value [MJ/kg] Waste fat 36.0 Paraffin 45.0 49.0 Biodiesel 37.0 Diesel 43.0 45.9 Heating oil EL 42.7 45.5 Heating oil L 42.0 44.8 Heating oil M 40.7 43.3 Heating oil S 40.2 42.7 Gasoline 42.5 Wood 15.1 18.8 Wood pellets 18.0 Paper 15.0 Peat 14.7 22.6 Lignite 19.7 20.9 briquettes Gas flame coal 27.2 29.3 Gas coal 29.3 31.0 Fat coal 31.0 32.2 Anthracite 31.0 31.8 Coke 30.1 30.5

Glycerol

Glycerol is a co-product in the industrial production of fatty acids and fatty acid esters which accumulates in the hydrolysis or transesterification of natural fats and oils and which is available in large quantities. The crude product is generally of purely technical quality, so that the chemical production process generally has to be followed by an expensive purification step in which the salts—above all sodium chloride—are removed by membrane processes and the water is removed by distillation.

In a number of cases, however, it is not only of economic advantage, but also desirable for application-related reasons to use crude rather than purified glycerol, particularly water-containing glycerol which accumulates in significant quantities in the production of biofuels (biodiesel), because combustion takes place more uniformly in this way. The glycerol prevents the water constituents from freezing out at low temperatures and blocking the engine. Accordingly, a preferred embodiment of the present invention is characterized by the use of glycerol containing water and/or salts. In this embodiment, the glycerol typically contains

(b1) 0.1 to 15, preferably 1 to 10% by weight water,

-   -   (b2) 0.1 to 5, preferably 1 to 2% by weight salts and     -   (b3) 0.1 to 1, preferably 0.5 to 0.75% by weight other organic         constituents.

Compositions

The compositions according to the invention may contain:

-   (a) 90.0 to 99.9, preferably 91 to 98, and more particularly about     95% by weight fuels and -   (b) 0.1 to 10.0, preferably 2 to 9, and more particularly about 5%     by weight glycerol.

Process for Improving Combustion Value and Combustion Performance

The present invention also relates to a process for improving the combustion value and combustion performance of liquid or solid fuels which is characterized in that glycerol is added to the fuels and the resulting compositions are then subjected to combustion. The compositions can be produced in various ways which leads to different embodiments of the same process according to the invention:

-   -   In a first embodiment, an emulsion is produced from liquid fuels         and glycerol, optionally using a suitable emulsifier, and is         introduced into the combustion space. This alternative is         suitable above all when the final preparation has to be stored         over a relatively long period, for example when the glycerol is         used as a diesel additive for a marine engine or when a         ready-to-use fuel mixture is to be dispensed at a filling         station. Depending on the nature of the liquid fuel and the         amount of water in the glycerol, it may be necessary to ensure         the homogeneity of the mixture by adding suitable emulsifiers in         small quantities, for example of 0.1 to 1% by weight, based on         the mixture. Nonionic emulsifiers are particularly suitable for         this purpose, including, for example, the following:         -   products of the products of the addition of 2 to 30 mol             ethylene oxide and/or 0 to 5 mol propylene oxide onto linear             C₈₋₂₂ fatty alcohols, C₁₂₋₂₂ fatty acids and alkyl phenols             containing 8 to 15 carbon atoms in the alkyl group and             alkylamines containing 8 to 22 carbon atoms in the alkyl             group;         -   alkyl and/or alkenyl oligoglycosides containing 8 to 22             carbon atoms in the alk(en)yl group and ethoxylated analogs             thereof;         -   a products of the addition of 1 to 15 mol ethylene oxide             onto castor oil and/or hydrogenated castor oil;         -   products of the addition of 15 to 60 mol ethylene oxide onto             castor oil and/or hydrogenated castor oil;         -   partial esters of glycerol and/or sorbitan with unsaturated,             linear or saturated, branched fatty acids containing 12 to             22 carbon atoms and/or hydroxycarboxylic acids containing 3             to 18 carbon atoms and addition products thereof with 1 to             30 mol ethylene oxide;         -   partial esters of polyglycerol (average degree of             self-condensation 2 to 8), polyethylene glycol (molecular             weight 400 to 5,000), trimethylolpropane, pentaerythritol,             sugar alcohols (for example sorbitol), alkyl glucosides (for             example methyl glucoside, butyl glucoside, lauryl glucoside)             and polyglucosides (for example cellulose) with saturated             and/or unsaturated, linear or branched fatty acids             containing 12 to 22 carbon atoms and/or hydroxycarboxylic             acids containing 3 to 18 carbon atoms and addition products             thereof with 1 to 30 mol ethylene oxide;         -   mixed esters of pentaerythritol, fatty acids, citric acid             and fatty alcohol and/or mixed esters of fatty acids             containing 6 to 22 carbon atoms, methyl glucose and polyols,             preferably glycerol or polyglycerol;         -   mono-, di- and trialkyl phosphates and mono-, di- and/or             tri-PEG-alkyl phosphates and salts thereof;         -   wool wax alcohols;         -   polysiloxane/polyalkyl/polyether copolymers or corresponding             derivatives;         -   block copolymers, for example Polyethyleneglycol-30             Dipolyhydroxystearate;         -   polymer emulsifiers, for example Pemulen types (TR-1, TR-2)             from Goodrich;         -   polyalkylene glycols and         -   glycerol carbonate.

Some preferred groups of emulsifiers are described in more detail in the following:

Ethylene oxide addition products. The addition products of ethylene oxide and/or propylene oxide onto fatty alcohols, fatty acids, alkylphenols or castor oil are known commercially available products. They are homolog mixtures of which the average degree of alkoxylation corresponds to the ratio between the quantities of ethylene oxide and/or propylene oxide and substrate with which the addition reaction is carried out. C_(12/18) fatty acid monoesters and diesters of addition products of ethylene oxide onto glycerol are known as lipid layer enhancing agents for cosmetic compositions.

Alkyl and/or alkenyl oligoglycosides. Alkyl and/or alkenyl oligoglycosides, their production and their use are known from the prior art. They are produced in particular by reacting glucose or oligosaccharides with primary alcohols containing 8 to 18 carbon atoms. So far as the glycoside unit is concerned, both monoglycosides in which a cyclic sugar unit is attached to the fatty alcohol by a glycoside bond and oligomeric glycosides with a degree of oligomerization of preferably up to about 8 are suitable. The degree of oligomerization is a statistical mean value on which the homolog distribution typical of such technical products is based.

Partial glycerides. Typical examples of suitable partial glycerides are hydroxystearic acid monoglyceride, hydroxystearic acid diglyceride, isostearic acid monoglyceride, isostearic acid diglyceride, oleic acid monoglyceride, oleic acid diglyceride, ricinoleic acid monoglyceride, ricinoleic acid diglyceride, linoleic acid monoglyceride, linoleic acid diglyceride, linolenic acid monoglyceride, linolenic acid diglyceride, erucic acid monoglyceride, erucic acid diglyceride, tartaric acid monoglyceride, tartaric acid diglyceride, citric acid monoglyceride, citric acid diglyceride, malic acid monoglyceride, malic acid diglyceride and technical mixtures thereof which may still contain small quantities of triglyceride from the production process. Addition products of 1 to 30 and preferably 5 to 10 mol ethylene oxide onto the partial glycerides mentioned are also suitable.

Sorbitan esters. Suitable sorbitan esters are sorbitan monoisostearate, sorbitan sesquiisostearate, sorbitan diisostearate, sorbitan triisostearate, sorbitan monooleate, sorbitan sesquioleate, sorbitan dioleate, sorbitan trioleate, sorbitan monoerucate, sorbitan sesquierucate, sorbitan dierucate, sorbitan trierucate, sorbitan monoricinoleate, sorbitan sesquiricinoleate, sorbitan diricinoleate, sorbitan triricinoleate, sorbitan monohydroxystearate, sorbitan sesquihydroxystearate, sorbitan dihydroxystearate, sorbitan trihydroxystearate, sorbitan monotartrate, sorbitan sesquitartrate, sorbitan ditartrate, sorbitan tritartrate, sorbitan monocitrate, sorbitan sesquicitrate, sorbitan dicitrate, sorbitan tricitrate, sorbitan monomaleate, sorbitan sesquimaleate, sorbitan dimaleate, sorbitan trimaleate and technical mixtures thereof. Addition products of 1 to 30 and preferably 5 to 10 mol ethylene oxide onto the sorbitan esters mentioned are also suitable.

Polyglycerol esters. Typical examples of suitable polyglycerol esters are Polyglyceryl-2 Dipolyhydroxystearate (Dehymuls® PGPH), Polyglycerin-3-Diisostearate (Lameform® TGI), Polyglyceryl-4 Isostearate (Isolan® GI 34), Polyglyceryl-3 Oleate, Diisostearoyl Polyglyceryl-3 Diisostearate (Isolan® PDI), Polyglyceryl-3 Methylglucose Distearate (Tego Care® 450), Polyglyceryl-3 Beeswax (Cera Bellina®), Polyglyceryl-4 Caprate (Polyglycerol Caprate T2010/90), Polyglyceryl-3 Cetyl Ether (Chimexane® NL), Polyglyceryl-3 Distearate (Cremophor® GS 32) and Polyglyceryl Polyricinoleate (Admul® WOL 1403), Polyglyceryl Dimerate Isostearate and mixtures thereof. Examples of other suitable polyolesters are the mono-, di- and triesters of trimethylol propane or pentaerythritol with lauric acid, cocofatty acid, tallow fatty acid, palmitic acid, stearic acid, oleic acid, behenic acid and the like optionally reacted with 1 to 30 mol ethylene oxide.

-   -   In a second embodiment of the process according to the         invention, the liquid fuels and the glycerol are homogenized in         a static mixer and the resulting mixture is introduced into the         combustion space. In this way, possible problems in the         production of homogeneous suspensions or emulsions are avoided,         because the two components are mechanically mixed immediately         before combustion. Alternatively, the two components can also be         separately introduced into the combustion space, for example by         spraying. This also guarantees an at least substantially         homogeneous distribution of liquid fuel and glycerol which is         useful for stable combustion. However, these variants do         presuppose the separate storage of both components, so that they         are probably more suitable for fixed combustion plants.     -   Where solid fuels are used, the preferred embodiment of the         process according to the invention is characterized in that the         fuels are sprayed or impregnated with the glycerol and then         introduced into the combustion space. Impregnation is the         simpler variant because storable final compositions are again         obtained in this way. If the incineration of household garbage         is to be supported by the addition of glycerol, application by         sprinkling, for example, immediately before incineration is more         suitable. As described previously, polymer waste, particularly         fiber waste from polyacrylate production, is also suitable as a         fuel. In this case, a preferred embodiment of the process         according to the invention is characterized in that the small         fiber fragments are dispersed in glycerol and—depending on the         quantity of fibers used—pumpable gels or slightly ductile shaped         bodies are produced in this way and introduced into the         combustion space.

In all these embodiments, glycerol is added to the fuels in quantities of about 0.1 to about 10% by weight, based on their weight.

Commercial Applications

As described above, the invention is directed to the addition of glycerol to solid or liquid fuels and to the beneficial effects achieved accordingly. The addition of glycerol increases the combustion value of the fuels, and enables combustion to take place more uniformly and with less slag formation. It is also possible to burn fuels which, hitherto, were only suitable for combustion to a limited extent, if at all. Accordingly, the present invention also relates to the use of glycerol for improving the combustion value and combustion efficiency of liquid or solid fuels. Combustion can take place either in fixed or in mobile combustion units such as, for example, spark-ignition engines, diesel engines, marine engines, aircraft engines, power stations or garbage incinerators. 

1) A fuel composition comprising: (a) a fuel; and (b) glycerol. 2) The fuel composition of claim 1 wherein the fuel is a liquid or a solid. 3) The fuel composition of claim 2 wherein the liquid fuel is selected from the group consisting of a fuel for spark-ignition or diesel engines, kerosene, a heavy oil for powering marine diesels, a heating oil and a fraction from refined petroleum. 4) The fuel composition of claim 2 wherein the solid fuel is selected from the group consisting of coal, coal dust, wood, synthetic fiber waste, a polymer and a mixed load for the incineration of garbage. 5) The fuel composition of claim 4 wherein the solid fuel is coal dust or synthetic fiber waste. 6) The fuel composition of claim 1 wherein glycerol contains water and/or salts. 7) The composition of claim 6 wherein the glycerol comprises: (1) about 0.1 to 15% by weight water, (2) about 0.1 to 5% by weight salts and (3) about 0.1 to 1% by weight other organic constituents. 8) The composition of claim 1 wherein the fuel is present in an amount of from about 90 to 99.9% by weight and the glycerol is present in an amount of from about 0.1 to about 10% by weight. 9) The composition of claim 1 which further comprises an emulsifier. 10) The composition of claim 9 wherein the emulsifier is nonionic. 11) The composition of claim 10 wherein the nonionic emulsifier is selected from the group consisting of an ethylene oxide addition product, an alkyl and/or an alkenyl oligoglycoside, a partial glyceride, a sorbitan ester, and a polyglycerol ester. 12) A process for improving the combustion value and performance of a liquid or solid fuel, which process comprises adding glycerol to the fuel to form a fuel composition and subjecting the composition to combustion. 13) The process of claim 12 wherein the fuel is present in an amount of from about 90 to 99.9% by weight and the glycerol is present in an amount of from about 0.1 to about 10% by weight. 14) The process of claim 12 which further comprises adding an emulsifier to form a fuel composition emulsion. 